Thirst

Can shipwrecked men survive if they drink sea water?

A vital function of the water in our bodies is to permit the kidneys to extract waste products from the blood in the form of urine. The chemical and physical processes involved in this function would take us beyond the scope of a general article. So we are centering our attention on the effect of the ingestion of the dissolved salts in sea water, predominantly sodium chloride or common salt. And the basic point is that the body uses only a very small amount of salt. Additional salt ingested must be excreted with the urine, using water which could be utilized by the body in other functions.

With the osmotic concentration of sea water only slightly below that of urine, the daily pint of sea water that the body will tolerate will only yield about 3/10 of a pint (143 c.c.) of free water for the excretion of other urinary constituents, as Dr. Homer W. Smith points out in his book From Fish to Philosopher. The amount of water actually needed for urine formation is about a pint, not to mention upward of 1500 c.c. more (over 3 pints) for sweat, if the individual is exposed to sun and wind. Yet 500 c.c., or about 1 pint, is the greatest amount of sea water that can be swallowed each day without gastrointestinal disturbance from the unabsorbable magnesium and sulphate. Consuming larger amounts, concludes Dr. Smith, would only lead to diarrhea and further dehydration and would hasten the end.

The most favorable report on the use of sea water is that of W. S. S. Ladell, printed in The Lancet, October 9, 1943. Ladell ran a series of experiments with a group of seventeen men on a “shipwreck ration” such as was carried in lifeboats. Some of the subjects drank sea water, others fresh water or fresh water plus sea water.

Ladell summarized the effects of drinking up to 400 c.c. (a little less than a pint) of sea water daily. The subjects were either totally or partially deprived of fresh water and were on the low-calorie and low-salt diet of the “man on the raft.” Thus they were getting almost all the salt their bodies used from the sea water they drank. Ladell’s conclusions were as follows, both for men drinking only sea water and for those using sea water as an “extender” for an inadequate fresh-water ration:

(a) At first, the subject retains the same amount of chloride that his body had lost before he began to drink sea water. Subsequently he excretes the full amount of chloride taken in. (b) The output of urine is increased, but there is a slight gain in the amount of the water in the body, because the extra water lost in the urine is less than the extra water taken in as sea water. (c) There is a gain in the total urea clearance.

(It should be noted that this experiment was performed in a laboratory where sweating would be at a minimum.)

Ladell’s experiment indicated that a slight advantage was to be gained when a man on limited fresh water or without any fresh water drank small quantities of sea water. However, the agency sponsoring the research did not recommend the drinking of sea water. Evidently it was felt that the small gain to be expected did not warrant the risk involved. Even if the survivor was able to hold his intake of sea water down to the limit recommended by Ladell (400 c.c., or less than 1 pint), the small volume of water gained in this way could not support human life indefinitely and would give little if any extension in survival time over that to be expected by a man drinking no water at all.

The sea-water enthusiasts argue that Dr. Alain Bombard drank sea water and survived; therefore, sea water must be beneficial. What was Bombard’s experience and how does it compare with that of shipwreck survivors? Bombard departed from Las Palmas, Canary Islands, on October 19, 1952, and landed at St. Lucia, Barbados, on December 23, 1952—a journey of 65 days. But 52 days after setting out, he boarded the S.S. Aroka, stayed an hour and a half, and had a meal. These 52 days represent his longest period of survival without outside help.